The goal of the proposed research is to use new membrane potential probes we have developed in our laboratory to learn about early macromolecular and ionic events that take place in the retinal rod. In particular we wish to develop a reconstituted rhodopsin-phospholipid vesicle preparation in which rhodopsin is "functional" in the physiological sense, i.e., rhodopsin photoregulates the release of transmitter from the vesicles. We want to identify the specific transmitter that is released from the discs (or from the vesicles) upon illumination and determine which spectroscopic intermediate of rhodopsin correlated with transmitter release. We want to study the effects of rhodopsin phosphorylation, temperature, vesicle lipid composition, and rhodopsin chromophore structure on the kinetics of transmitter release from vesicles. We plan to use our potential probes to determine the ion transport properties of disc membranes and rod outer segment plasma membranes. Finally, we want to develop membrane voltage probes that can be routinely used by neurophysiologists to study receptor potentials in visual systems where the use of microelectrodes is impractical.